1) Field of the Invention
The present invention is related to the field of semiconductor manufacturing and more specifically to a method and apparatus for forming an epitaxial titanium silicide film by low pressure chemical vapor deposition.
2) Discussion of Related Art
Semiconductor devices are made up of literally millions of discreet devices which are interconnected together to form functional circuits, such as microprocessors, memories and programmable logic devices. In order to improve circuit performance, the fabrication processes generally utilize low resistance metal films such as silicides to form low resistance contacts to devices. Titanium silicide deposited by low pressure chemical vapor deposition has been proposed to reduce the contact resistance of devices.
FIG. 1 is an illustration of a current CVD apparatus which can be used to deposit a titanium silicide film on a semiconductor wafer or substrate. A susceptor 120 divides a chamber 112 into one portion which is below the susceptor 124 and a second portion which is above the susceptor 122. The susceptor 120 is generally mounted on a shaft 126 which rotates the susceptor about its center to achieve a more uniform processing of the wafer. A flow of processing gas such as deposition gas 115 is provided into the upper portion 122 of the chamber. The chamber generally has a gas inlet 178 at one side thereof and a gas exhaust passage 116 at the opposite side to achieve a flow of processing gas across the wafer. The susceptor 120 is heated in order to heat the wafer to a desired deposition temperature. One method to heat the susceptor is by the use of lamps 134 provided around the chamber and directing the light into the chamber and onto the susceptor 120.
In a method of depositing titanium silicide on a wafer by thermal chemical vapor deposition, a deposition gas 115 containing titanium chloride (TiCl4) and a silicon source gas, such as SiH4, is fed into the reaction chamber 112. As deposition gas is fed into the chamber, it is heated by preheat ring 128 and susceptor 120 and wafer and reacts to form titanium silicide. Such a process can be used to form high quality polycrystalline titanium silicide films. In certain applications, however, a polycrystalline titanium silicide film may not be optimal and an epitaxial (monocrystalline) titanium silicide film is desired. Unfortunately, however, there is presently no technique to form an epitaxial (monocrystalline) titanium silicide film by thermal chemical vapor deposition. Presently, only plasma enhanced chemical vapor deposition (PECVD) has been used to deposit epitaxial titanium silicide.
Thus what is desired is a method and apparatus for forming an epitaxial titanium silicide film by thermal low pressure chemical vapor deposition.